I know it's stupid, but it's S.O.P. for many countries, including Canada, and probably the US as well. Don't think it is just some Korean aberration- it isn't.

As to why, I suspect it's to curb people just showing up on tourist visas and looking for work. In other words it's ineffective, because many people around the world do just that, but it's still on the books.

Often the regulation of having the potential employee get a work visa (or apply for one) is coupled with a regulation that the employer must show evidence that an attempt has been made to fill the position with someone already qualified to work in the country. I imagine this varies depending on the position and the country, and I'm sure there are many exceptions.

I personally know of two examples of this from 2 countries other than Korea but I'm not going to bother typing them all out unless someone is actually interested.

I think it's wrong to make people leave once they've already been working, and their just changing schools/contracts.

That's where Korea lags behind Japan, for example. So many Koreans have bugs in their bonnets about competition with Japan, perhaps if everyone goes around saying "Japan is a better country because that's the way it's done there" enough times Koreans might actually give some serious thought to change. Whaddya say, CPA?